An ostomy (also referred to as a colostomy, ileostomy or urostomy) is a type of surgery required when a person loses normal bladder or bowel function due to birth defect, disease, injury or other disorder. Cancer patients account for about 80 percent of ostomies. Following an ostomy, bodily waste needs to be expelled through a stoma (surgical opening) on the abdominal wall and into a special appliance called an ostomy bag.
Depending on a patient's diet, age, diagnosis, activity level, and other variables, these wastes can contain significant amounts of gases, such as amines, ammonia, and mercaptans. These gases can inflate the ostomy bag, creating concern or discomfort for the patient, and compromise the seal between the skin and the bag itself.
In the past, ostomy bags have been provided with deodorizing gas filters so that flatus gases can be vented from the bag to reduce or prevent ballooning and, at the same time, to deodorize the escaping gases. In an effort to prevent such a filter from becoming clogged and rendered ineffective by liquid and/or solid body waste material within the bag, it has been common either to secure the filter to the outside surface of the bag over a vent opening, or to provide protection for an internally-mounted filter in the form of a porous membrane that extends over the filter. Typically this internally-mounted filter is hydrophobic and may also be oleophobic.
Ostomy bag filters may be of the axial flow type, as shown in FIG. 1, or more commonly the so-called radial flow type or lateral flow type, as shown in FIG. 2. In the axial flow filter 100, the air to be filtered flows in a straight path from a first side 104 to a second side 106, directly or axially though the filter media 108. In contrast, the term lateral flow or radial flow means that the gases flow along the plane of a relatively flat filter, as shown in filter 200 of FIG. 2. In FIG. 2, the gases flow from a first side 204 to a second side 206 by entering the filter media 208 at its outer edge 210 and flowing toward a center 212 of the filter media. Filter layers can also be configured so that the gas flows from one end of a filter media to another end, or in many different types of flow paths. For ostomy bag applications, a filter of the radial or lateral flow type is most common because it allows for the construction of a low-profile filter that also provides an extended flow path for deodorizing the flatus gases.